In Japanese Patent No. 2816784, the consumed yarn length of each loop to be knitted from the changeover position, which is located on the knitting fabric for changing over a knitting yarn to an after-processed yarn, to the actuating position of the yarn processing device is added reversely to the order of knitting, whereby the total yarn length (remaining length to be knitted W) is obtained from knitting data. Furthermore, the yarn length between the yarn processing position and the knitting needle that is the actuating position of the yarn processing device (yam guide length L) is obtained. The yarn processing is performed when the remaining length to be knitted W and the yarn guide length L match. Also, Japanese Unexamined Patent Application Publication No. 2002-227064 discloses that yarn is held between a pair of rollers to control the amount of yarns to be fed, and the yarns are fed to the yarn feeder side.
Incidentally, a knitting machine, such as a flat knitting machine, is provided with a tension arm to buffer yarn before a needle bed. Since the buffer length (slack length) of the yarn on the tension arm constantly changes, considered is to monitor the angle of the tension arm in order to accurately obtain the timing for processing the yarn using a yarn processing device. However, it is not enough to simply obtain the buffer length on the tension arm. It is often the case that if the pattern of deceleration of a carriage or the like is defined such that the carriage or the like is stopped at the point of time when the yarn guide length obtained after correcting the buffer length on the tension arm matches with the remaining length to be knitted W, the tension changes during a processing of stopping the carriage or the like and the buffer length on the tension arm also changes, whereby the yarn guide length no longer matches with the remaining length to be knitted W at the point of time when the carriage is stopped.